1. Field of Invention
This invention generally relates to vehicle occupant restraints. More specifically, this invention relates to seat belt restraint systems.
2. Prior Art
Vehicle occupant restraints, including seat-belt-restraint-systems and devices, are important and well-known components of vehicle safety systems. When a vehicle experiences severe impact, a properly belted-in occupant is held in place by the webbing, thereby avoiding many serious, if not fatal, physical collisions with vehicle interior and/or being thrown from the vehicle. Since their introduction seat-belt-restraint-systems have saved countless lives and reduced the severity of injury in countless more.
Initially seat-belt-restraint-systems provided only a belt across the lap of the occupant. This is the so-called “two-point” seat-belt-restraint-system. Although an improvement over no belt at all, such lap only seat-belt-restraint-systems did nothing to restrain the very dangerous occupant's upper body motions. Therefore, head, neck and back injuries were very common among victims of vehicle collisions who were wearing only a lap belt.
A further improvement to the two-point seat-belt-restraint-systems came with the introduction of a third point of fixation. A second belt, shoulder belt, is provided. The upper end of the shoulder belt is extendable and retractable to the upper portion of the vehicle adjacent the occupant's shoulder. This is the third point of fixation. The lower end of the shoulder belt extends to the lap belt via a sliding seat belt latch. This seat belt latch is engageable with a seat belt buckle anchored to the vehicle and disposed on the inboard side of the occupant. The other end of the lap belt is anchored to the vehicle and disposed on the outboard side of the occupant. These improved seat-belt-restraint-systems are referred to as “three-point” seat-belt-restraint-systems because they provide three fixation points for the webbing. Three-point seat-belt-restraint-systems improve the performance of occupant restraint by restricting the occupant's upper body and lower body motions.
Many patents have been issued to three-point seat-belt-restraint-systems.
U.S. Pat. No. 6,336,662 to Kurita et al., issued on Jan. 8, 2002, describes a three-point seat belt system with a tongue hooking mechanism for a seat belt incorporating a buckle disposed on a side of a seat adjacent to a central portion of a cabin of a vehicle.
U.S. Pat. No. 6,334,628 to Newball et al., issued on Jan. 1, 2002, describes a ceiling retractable three-point seat belt system for restraining an occupant in a vehicle center seat.
U.S. Pat. No. 6,328,386 to Good, issued on Dec. 11, 2001, describes a detachable three point seat belt system, which can be detached to allow the center seat back to be pivoted down.
U.S. Pat. No. 6,302,442 to Shimozawa, issued on Oct. 16, 2001, describes an attachment structure of a three-point seat belt system for a rear seat in which a seat belt retractor can be attached without causing an increase in vehicle weight and an increase in manufacturing cost.
U.S. Pat. No. 6,234,529 to Ellison et al., issued on May 22, 2001, describes a three-point seat belt system with its shoulder belt extendable and retractable to the rear roof for the use by a rear center seat occupant.
U.S. Pat. No. 6,116,696 to Widman et al., issued on Sep. 12, 2000, describes a detachable three-point seat belt system having an interlocking mechanism that requires the wearer to reattach a detached system to the seat prior to fastening the seat belt over the wearer's body.
U.S. Pat. No. 5,176,402 to Coulon, issued on Jan. 5, 1993, describes a three-point seat belt system, which is mounted to the seat frame removably mounted to a vehicle.
U.S. Pat. No. 4,289,328 to Repp et al., issued on Sep. 15, 1981, describes a three-point seat belt system that has a shoulder belt extendable and retractable to the vehicle door.
Three-point seat-belt-restraint-systems have the advantages of convenience of use and good occupant restraint performance. However, There are some important drawbacks. For example, a conventional three-point seat-belt-restraint-system has a shoulder belt end extendable and retractable to the upper portion of a vehicle, most preferably, to pillars or roof rails. These positions are natural choices of seat-belt-restraint-system design because pillars and roof rails are two of the strongest portions of vehicle structures for supporting the belt loads during accidents. But these positions are not close enough to the occupant's shoulder for superior restraint performance, especially for lateral impact accidents, rollover, etc.
Seat-mounted three-point seat-belt-restraint-systems correct the deficiency of pillar/roof-rail mounted seat-belt-restraint-systems by moving the fixation point of the shoulder belt to the upper portion of the vehicle seatback. However, by doing so, they introduce an inevitable drawback. The performance of occupant restraint is, now, solely depending on the vehicle seat. All loads imparted through the restraint system during accidents will be withstood by the seat structure and then by the floor and vehicle underbody. Typically, during a vehicle frontal impact accident, the stiffness of the vehicle seat and that of the floor underneath the seat play a significant role in the performance of occupant restraint. Reinforcement of the seat and the floor underneath the seat to reduce the seat excursion during an accident incurs added weight and cost. This problem is more important for small vehicles, which do not have much flexibility in weight, space, cost, etc.
Currently in the market, only limited number of large vehicles, like trucks, sports utility vehicles, etc., is using seat-mounted three-point seat-belt-restraint-systems.
Seat-mounted four-point seat-belt-restraint-systems have the advantage of good performance of occupant restraint by restraining the occupant to the vehicle seat through two shoulder belts, one on each side of the occupant. However, there are some important drawbacks. First, it is inconvenient to use, thereby discouraging its application. When an occupant sits in a vehicle seat, he/she needs to reach his/her back to get the shoulder belts on both sides. Second, as discussed before about seat-mounted three-point seat-belt-restraint-systems, the performance of occupant restraint solely depends on the vehicle seat. Small vehicles might have difficulties in achieving good safety performance in frontal impact tests and real-world accidents.
Some patents have been granted to four-point seat-belt-restraint-systems.
U.S. Pat. No. 6,375,270 to Sullivan et al., issued on Apr. 23, 2002, describes a seat-mounted four-point seat-belt-restraint-system, which can be adapted for use as a three-point seat-belt-restraint-system.
U.S. Pat. No. 6,076,894 to Busch, issued on Jun. 20, 2000, describes a seat-mounted four-point seat-belt-restraint-system, which has two lap belt portions.
U.S. Pat. No. 5,123,673 to Tame, issued on Jun. 23, 1992, describes a seat-belt-restraint-system, which includes a three-point seat-belt-restraint-system forming a lap belt and a shoulder belt and further includes a second shoulder belt to form a four-point seat-belt-restraint-system.
Currently in the market, very few vehicles are using seat-mounted four-point seat-belt-restraint-systems, except racing cars.
Therefore, it remains desirable to provide a seat-belt-restraint-system that can provide the performance of occupant restraint of both three-point and four-point seat-belt-restraint-systems without losing the convenience of use of three-point seat-belt-restraint-systems. It remains desirable to provide a seat-belt-restraint-system that is safer, more comfortable and convenient to use, and simpler and less expensive to manufacture, for general public against various accident modes.